1. Technical Field
The present invention concerns a method and holding device for the clamping of an insert into a cutting tool for metal removal machining.
2. Description of the Background Art
Many different tools are used within the metal removal machining for turning and milling. The use of tools that include a hard metal insert is previously known, e.g., a so called throw-away insert, which is clamped or locked in a tool holder. The inserts are often relatively small, usually around a maximum of ten millimeters, due to the costs of the material and of the manufacturing, and also to make it possible to gain access to and carry out confined and small machining operations on a work-piece.
Clamping of an insert into a tool holder can be achieved, for example, by the holder containing an upper and a lower adjustable locking element, into the opening of which the insert is placed, followed by the locking elements being arranged with the aid of a locking screw or similar to lock the insert firmly. A number of tools with various more or less technically complicated solutions for the arrangement for clamping into the holder are known. The adjustment and locking of the insert into the holder should be as simple as possible for reasons of efficiency. The insert must be firmly clamped. The clamping force should thus preferably be distributed over a large area. The dimensions of the holders must often be small in the vicinity of the cutting region due to the requirement of achieving good accessibility. However, the smaller the holder is, the less is the rigidity obtained in the tool.
The design of interacting, prefabricated grooves or similar on the insert and the holder is also known. The purpose of these grooves is, among other things, to give a more rigid design, to prevent sideways movement of the insert and to give simpler positioning of the insert in the holder. On the other hand, problems arise when manufacturing grooves that are to interact between the insert and the holder, since this requires complicated adjustment of tolerances and an identical grinding of the grooves in both the insert and the holder, something that of course also is expensive. The alignment of lines on two objects, during which two opposite grooves must fit into each other, places high demands on accuracy during manufacture and assembly. The problem is to obtain a correct alignment and a rigid clamping of the insert into the holder also in the locked condition. A further problem associated with prefabricated grooves of various types is that various types of inserts cannot automatically be gripped into any holder. All the different types of inserts and tool holders in which this type of clamping is to be applied, that is the alignment of lines on two objects, must be provided with equivalent grooves.
A tool for metal removal machining is previously known from U.S. Pat. No. 5,054,967 that includes a holder and an insert to be clamped in the holder. The insert can be provided with grooves, and the holder can thus be provided with matching ridges. According to another embodiment, the insert is coated on its bottom surface with a soft metal layer that has greater friction than the opposite surface in the holder with which the insert interacts. The design according to U.S. Pat. No. 5,054,967 does not specify a solution to the problems that have been described in the description of the prior art given above.
EP-A1-0802006 concerns a cutting tool that contains a holder and an insert. Sharp-edged, sharp, roof-shaped protrusions with an angle at the point of between 60xc2x0 and 90xc2x0 are arranged on the surfaces of the insert. The roof-shaped protrusions on the insert are pressed down into the steel surface of the tool with the aid of the pressure that loads the insert when the clamping screw is tightened, whereby the surface of the tool is plastically deformed. The design of the insert with the sharp-edged roof-shaped protrusions means that the cutting tool will xe2x80x9cride up onxe2x80x9d the roof-shaped protrusions. This entails a poorer locking of the insert in the tool holder. Thus the construction according to EP-A1-0802006 does not specify a solution to the problems that have been described in the description of the prior art given above.
The intention of the present invention is to achieve the clamping of an insert in a tool holder for metal removal machining, that is both rigid and simultaneously simple and to eliminate the said disadvantages described in the description of the prior art given above. One intention is thus to achieve a method and a design that simplifies the adjustment and increases the clamping force of the insert in the tool holder. Furthermore, an intention is to create improved fixing and locking. A further intention of the present invention is to eliminate any relative motion between the insert and the holder. A further intention is a method and a design of the tool by which it is simple to exchange insert and in which many types of inserts can be used, such as insert for milling, turning, etc. A further intention is to achieve a cost-effective production of the insert and the holder.
The method and the device according to the present invention solve the above-mentioned problems, and are characterized in the said purposes by that which is made clear in the claims. Thus the method according to the present invention concerns the locking of an insert into a tool for metal removal machining. The tool comprises an insert with an upper contact surface or section and a lower contact surface or section. The insert is arranged in a holder whereby the holder comprises a holder body and a clamping device. The holder body has a lower contact surface or section. The insert is arranged such that the lower contact surface or section of the insert is brought into contact or engagement with the lower contact surface or section of the holder and the clamping device is brought into engagement with the upper contact surface or section of the insert. At least one of the contact surfaces of the insert is provided or designed with protrusions or irregularities in the form of rounded cones, teeth or the like, which are brought to press or be pressed into the opposite surface or section of the holder during deformation of the same when clamping the insert.
One advantage with this solution according to the present invention is that the clamping of the insert into the holder is significantly improved in relation to conventional methods and designs. The clamping of the insert becomes very rigid. During machining, the cutting force contributes to an increased locking of the insert into the holder. By the arrangement of the insert into the holder, the protrusions of the insert are, at least partially, or wholly, pressed into and deform the surface of the holder. This occurs during a first phase through a clamping force that is brought to act on the insert by means of a clamping device, but above all it occurs during a second phase when the cutting force acts on the insert. In this way, differences in hardness of different materials of the insert and the holder are exploited. The clamping force is distributed over a very large area, since a considerable or complete contact of surfaces is achieved along the complete surface profile of the insert. This is particularly true when the contact surface of the insert is not flat, since this then by its shape will be much longer than a flat surface. The absorption of force in all directions is achieved in the interface layer between the interacting surfaces.
Furthermore, an accurate fixing is achieved, together with an accurate locking according to the present invention. A further advantage is that no adjustment of tolerances needs to be considered during interaction between the surfaces of the insert and those of the holder. Since no complicated setting of tolerances of the surfaces of the insert and the holder take place, no problems with the adjustment of the insert arises. In this way, it is very simple and easy to exchange insert in the holder. The principle can be used for essentially all types of inserts. In addition, any relative motions between the insert and the holder are eliminated in the method and the design according to the present invention. Furthermore, a very great resistance to withdrawal of the insert from the holder is achieved with the design according to the present invention.
The principle with which the insert is clamped into the tool holder can be likened to that of shape-associated locking. Neither is the surface of the holder subject to significant wear on repeated clamping of the insert. The tolerances of the protrusions on the insert are normally of the order of a few thousandths of a millimeter. These precise tolerances mean that the protrusions enter the same positions on clamping, into depressions that have been created during deformations during previous clampings of an insert with similar protrusions, whereby the surface of the insert and the surface of the holder are again deformed together.
The present invention also concerns a cutting tool for metal removal machining. The tool comprises of a holder and an insert intended to be arranged in the holder. The insert comprises an upper contact surface or section and a lower contact surface or section. The holder comprises a holder body and a clamping device, where the holder body has a lower contact surface or section. The insert is arranged such that the lower contact surface or section of the cutting tool is in contact with and interacts with the lower contact surface of section of the holder. Furthermore, the insert is arranged in the holder such that the upper contact surface or section of the insert is brought into contact with and interacts with a lower surface of the clamping device. At least one of the contact surfaces of the insert comprises a protrusions in the form of rounded cones, teeth or the like, which are arranged to be at least partially pressed into opposite surface and deform the surface of the holder when the insert has been arranged and is subject to load in the holder.
The present invention also concerns an insert for metal removal machining. The insert comprises an upper contact surface or section and a lower contact surface or section, and it includes side surfaces between the contact surfaces. The insert comprises at least one cutting edge in the interface between an upper cutting surface and a front surface. The insert is intended to be arranged and subject to load in a holder. At least one of the contact surfaces of the insert comprises protrusions in the form of cones, teeth or the like, which are intended to be at least partially pressed into an opposite surface of a holder and to deform the surface of the holder when arranged and/or when the insert is subject to load.
The protrusions in the contact surface or section of the insert according to the present invention can be formed as rounded bumps, cones, teeth, pyramids, barbs, humps or the like, which are elevated with respect to the contact surface. It is suitable if the protrusions are in the form of rounded cones, teeth or pyramids. The concept of xe2x80x9croundedxe2x80x9d is used to denote the fact that the extreme top of the protrusion has a well characterized rounding-off such that the top of the protrusion does not split when the insert is subject to cutting forces. Thus, it is suitable if the top of the protrusion has a radius that lies within the interval from about 0.05 mm to about 0.2 mm, and preferably within the interval from about 0.08 mm to about 0.1 mm. The protrusions can have a height from a few tenths of a millimeter up to a few millimeters. It is suitable if the height of the protrusions is within the interval from about 0.01 mm up to about 2.0 mm, and preferably within the interval from about 0.05 mm to about 0.5 mm. The density, the distribution, between the protrusions, that is, the distance between two protrusions arranged next to each other, can be from a few hundredths of a millimeter up to several millimeters, and preferably within the interval from about 0.8 mm up to about 12 mm.
It is suitable that the protrusions are evenly distributed and spread over, or arranged along, the full extent of the contact surface or section of the insert. According to one preferred embodiment, only a part of the lower surface of the contact surface or section of the insert is equipped with rounded protrusions. It is suitable if the protrusions cover a part from about 10% up to about 50% of the area of the lower surface of the cutting tool, and preferably from about 20% up to about 33%. Since the protrusions only cover a part of the lower surface of the insert, it is suitable that these should be placed at the front edge of the insert, that is, on that area of the lower surface of the insert that faces the short side of the holder body adjacent to the object that is to be machined. In this way, it can be ensured that the protrusions are completely pressed down into the surface of the holder body and in this way achieve complete contact between the surfaces of the insert and the holder body.
The protrusions must be harder than the material of the opposite contact surface or section of the holder, since the protrusions are to sink or be pressed, at least partially, into the opposite contact surface or section of the holder when the contact surface or section of the insert with protrusions is placed into it. It is suitable if the protrusions are the same material as the insert.
The protrusions of the insert are to be completely pressed into the surface of the holder according to one embodiment of the method, the insert and the tool according to the present invention, whereby an essentially total contact of surfaces is obtained along the complete surface profile of the insert. xe2x80x9cTotal contact of surfacesxe2x80x9d is used to denote essentially the complete lower surface of the insert being in contact with the surface of the holder.
The insert is manufactured from a material that is suitable for metal removal machining, such as, for example, a hard-metal, high-speed steel, ceramic or a ceramic material. The inserts may be coated or uncoated.
The clamping device and the holder body are manufactured in the conventional manner from steel or another suitable material, such as, for example, aluminium.
The holder includes a holder body and a clamping device, such as a clamp device. The clamping device is intended to exert a force against the insert on attachment of the insert in the holder body. The lower contact surface or section of the holder and the lower surface of the opposite insert, the lower contact surface or section, may be wedge-shaped, bowl-shaped, plane, or another geometric shape suitable for the purpose.